EP3623894B1

EP3623894B1 - Agv having dynamic safety zone

Info

Publication number: EP3623894B1
Application number: EP18194300.2A
Authority: EP
Inventors: Niels Jul Jacobsen; Soeren Nielsen
Original assignee: Mobile Industrial Robots AS
Current assignee: Mobile Industrial Robots AS
Priority date: 2018-09-13
Filing date: 2018-09-13
Publication date: 2022-11-23
Anticipated expiration: 2038-09-13
Also published as: WO2020053088A1; US20220043452A1; US11845415B2; EP3623894A1; CN112673329A; CN112673329B

Description

FIELD OF THE INVENTION

The present invention relates to an AGV having dynamic safety zone based on the payload carried or towed by the vehicle. More specifically, the invention relates to a way of determining and promoting safety of a robotic payload.

BACKGROUND OF THE INVENTION

For autonomous (guided) vehicles (AGV), i.e. mobile driverless robots, there is a problem that the braking distances of the robots in motion are often incorrect and not reflecting the true braking distance. The braking distance used in the computer software that monitors and calculates if the vehicle is on collision course towards obstacles is often a value only depending on robot speed or static figures not reflecting the actual state of the vehicle and hence the actual braking distance. The incorrect braking distances used in the calculations results in either a risk of collision or an autonomous vehicle that drives too slow compared to what is possible while still operating safely.
In some robots the braking distance is not continuously calculated but instead a safety system continuously monitors i) the driving speed from motor/wheel encoder input, and ii) obstacle distance from scanner or other sensor input. Based on the driving speed a physical safety zone around the robot is defined and continuously evaluated from the scanner/sensor input if there are obstacles inside the safety zone and when this is the case then reduce speed by motor control or apply a braking mechanism to avoid collision. In such a system the incorrect braking distances will also result in either collision or unnecessary braking or reduction of speed.
Automated guided vehicles (AGV) may be used to transport payloads along a predetermined route without real-time human assistance. For example, an AGV can transport items such as heavy vehicle components like engines, chassis, etc. along a route on a manufacturing plant floor to deliver the payload from one location to another to allow various manufacturing operations to be performed thereon. Typical plant floors or other surfaces upon which AGVs operate may include irregularities that do not affect their normal operation as they travel from one location to another. For example, some AGVs may include shock absorbing or similar systems to allow the AGV to traverse irregular surfaces without disturbing the payload. Meanwhile, when adding a cart/trolley to be towed by a robot the braking distances are increased. Mobile Robots are equipped with safety zones. When an object is visible inside the safety zone the robot safety system activates and stop the robot before collision with the object. Hence the safety zone must always be larger than the braking distance. The safety system is normally configured to change size of safety zone depending on velocity. Robots do not change safety zones based on attachment of cart.
US 2017/0291315 discloses sensors for detecting payload and adjusting the robots velocity etc but it does not envisage changing safety zones.
WO 2017/050358 A1 describes a method of guiding a mobile robot on a path within an environment that comprises one or more obstacles. The method includes i) determining the obstacle(s) in said environment, ii) determining a speed of displacement of said mobile robot depending on the determined obstacle(s), iii) determining one or more safety fields around the mobile robot depending on said variable speed, iv) dynamically determining an envelope comprising both said variable safety fields and said mobile robot, said envelope being variable if the at least one safety field varies, v) applying a protection management procedure to prevent that at least one obstacle enters into the envelope, said protection management procedure comprising dynamically adapting the envelope so that the zone defined by said envelope remains free from obstacles.
JP H08-006640A describes a method of controlling the operation of an AGV that performs a pace-making function along an assembly line.

SUMMARY OF THE INVENTION

The above mentioned problem associated with the prior art solutions has been solved by the present invention by mounting on the AGV (designed to tow a cart) a proximity sensor or mechanical switch to gripper or bottom of a cart for detection of when a cart is attached or when there is mass in the cart. This sensor input is used for adjusting the safety zones of the robot in order to match the changed brake distances. In an alternative embodiment of the present invention a payload of robot is detected by means of a sensor and/or a load cell and is used to adjust the safety zones depending on impact on brake distances. Thus, the solution to the problem is to take dynamic inputs from the vehicle that can be used to determine the braking distance more accurately and adjust the safety zones or values used for calculating the braking distance or collision check. Accordingly, the present invention provides automatically guided vehicle (AGV) comprising drive wheels; a robot body mounted on said drive wheels; and optionally a cart attaching mechanism mounted on said robot body for coupling the cart to said vehicle. A scanner or sensor is provided for the detection of any obstacles inside a safety zone of the path pursued by the vehicle, and a control system is used for navigation and receiving information from the scanner or sensor with respect to obstacles. Importantly, the control system is not necessarily confined to a single system but may be composed by multiple sub-systems, each performing specific tasks, yet coordinated between the multiple sub-systems, e.g. a security system as one sub-control systems with another sub-system controlling navigation and speed of the robot.
The control system configured to dynamically set safety brake distances for the vehicle based on payload mass, including payload mass placed either on the vehicle or payload mass being towed, such as in a cart, by the vehicle. In that respect the vehicle is configured to detect if a payload mass differs significantly from a preset payload mass towed and/or carried by the vehicle, the preset payload mass corresponds to a preset safety brake distance, and if a payload mass different from the preset payload is detected, the control system is automatically updated to adjust:

the speed of the vehicle based on preset safety brake distance information associated with the detected different payload mass; and/or
increase the safety zone or switch to a safer safety zone in order to avoid collision with any obstacles.

Further, the AGV may include a cart attaching mechanism mounted on said robot body for coupling the cart to said vehicle; and optionally a proximity sensor mounted on the robot body for detecting if a cart is towed by the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1A-1D show a flow diagram of the steps performed by the AGV in order to dynamically change its safety zones in response to any obstacles.
Figures 2A-2C show the principles of calculating ground level inclination or declination.
Figure 3 shows an embodiment of the AGV towing a trailer.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the invention solves the problem of different braking distances with or without the vehicle towing a cart/trailer. This is achieved by utilizing a sensor, which detects if a cart is attached or not. The sensor can be a simple proximity sensor which uses light (IR, laser or similar), capacitance, inductance or mechanical movement (switch). When the sensor indicates that a cart is attached the safety zones are changed to other preset values that reflect the larger braking distance or the values used for calculating the braking distance or check the collision is changed.
Another aspect of the invention solves the problem of higher braking distances when the vehicle has a heavy payload. This is achieved by utilizing a load sensor in the payload area of the vehicle or on the wheel suspension area, which detects the mass of the payload or total mass of the vehicle. The load values can then be used for selecting different safety zones from a number of different tables of braking distance for different speeds or be calculated via Newtonian rules, each table representing a different payload range. Alternatively the payload figure can be used for selecting different values for calculating the braking distance or check the collision. A variant of the method is to have more than one payload sensor and from these inputs determine the gravitational centre and the total payload and use these values for selecting the safety zones or calculating the braking distance or the collision check.
The third aspect is to decide the payload, towing mass and braking distance from an acceleration and deceleration test. At various intervals, i.e. after every stop of a certain duration or similar, the robot will start driving with a known predetermined motor torque and from the motor/wheel encoder input it can calculate the acceleration of the vehicle. After a small acceleration the vehicle can apply a predetermined period of braking or free running and from the encoder input in this period calculate the deceleration. From the acceleration and deceleration figures the inclination/declination of the ground can be determined and based on this information the braking payload, towing mass, and braking distance can be calculated by the robot software.
Referring to Figure 1A-1D there are shown flow diagrams, which reflect the steps carried out by the controller of the AGV in three alternative modes.
In accordance with Figure 1A there is provided a solution to the problem of different braking distances with or without the vehicle towing a cart/trailer is to have a sensor which detects if a cart is attached or not. The sensor can be a simple proximity sensor which uses light (IR, laser or similar), capacitance, inductance or mechanical movement (switch). When the sensor indicates that a cart is attached the safety zones are increased to other preset values that reflect the larger braking distance or the values used for calculating the braking distance or check the collision is changed.
As shown in Figure 1B the problem of higher braking distances when the vehicle has a heavy payload is solved by having a load sensor in the payload area of the vehicle or on the wheel suspension area which detects the mass of the payload or total mass of the vehicle. The load values can then be used for selecting different safety zones. Alternatively the payload figure can be used for selecting different values for calculating the braking distance or check the collision. A variant of the method is to have more than one payload sensor and from these inputs determine the gravitational centre and the total payload and use these values for selecting the safety zones or calculating the braking distance or the collision check.
In Figure 1C, which constitute the third alternative, is to decide the payload or towing mass from an acceleration and deceleration test. At various intervals, i.e after every stop of a certain duration or similar, the robot will start driving with a known predetermined motor torque and from the motor/wheel encoder input it can calculate the acceleration of the vehicle. After a small acceleration the vehicle can apply a predetermined period of braking or free running and from the encoder input in this period calculate the deceleration. From the acceleration and deceleration figures the inclide/declide of the ground can be determined as well as the payload or towing mass.
The ground level inclination or declination can be calculated by performing an acceleration and a deceleration of the robot with known forces. By performing both an acceleration test followed immediately be a deceleration period of either free running or known braking force the levelness of the ground plane can be calculated, see Figures 2A-2C. The ratio between acceleration and deceleration visualized by the angle alpha is proportional to the inertia and thereby the mass of the robot including payload and/or attached cart. Hence by calculating alpha and determine for a given system the relationship between alpha and total mass the mass can be calculated from the acceleration and deceleration data.
An alternative to making both acceleration and deceleration tests is to only perform an acceleration test and combine this with data from a gyroscope sensor.
Referring to Figure 3 there is shown a cart attached to the robot. The cart attaching mechanism has automatically made a coupling with the cart and transports it to a destination. In Figure 2 the automatically guided vehicle is used for towing (or pushing) a wheeled cart having at least four wheels and provided with a cart frame, the vehicle comprising drive wheels; a robot body mounted on said drive wheels; a control system utilizing a navigational system; a cart attaching mechanism mounted on said robot body for coupling the cart to said vehicle; at least one proximity sensor mounted on the robot body, said control system coupled to said at least one proximity sensor for adjusting the calculated robotic position and detecting any obstacles. The cart attaching mechanism includes a trailer arm that is freely rotatable in a horizontal plane, said arm mounted in a pivot point on the robot body in one end and provided with a gripping portion in the other end for gripping and holding the cart to be towed. A proximity sensor placed on the rear side of the AGV may detect whether or not a cart is attached. A load detector placed below the cart may measure the load carried and transfer this information to the controller of the AVG to dynamically adjust the safety zones of the robot in order to match the increased brake distances.
The mobile robot of the present invention includes a chassis, a drive system disposed on the chassis and configured to maneuver the robot over a work surface. It may further comprises a control system connected to the drive system. Furthermore, the robot (AGV) may have a deck system including a payload deck configured to receive a removable payload.
For the sake of completeness it is noted that the present disclosure uses the term automatically guided vehicle (AGV) for any mobile robot having a navigation system, which may be guided by e.g. vision, magnets, geoguidance, gyroscope, and lasers. It is therefore understood that the term also comprises Autonomous Mobile Robots (AMR).

Claims

An automatically guided vehicle comprising:
drive wheels;

a robot body mounted on said drive wheels;

a scanner or sensor for the detection of any obstacles inside a safety zone of the path pursued by the vehicle; and

a control system configured to
receive information from the scanner or sensor with respect to obstacles,

characterized in that the vehicle is configured to calculate a payload or towing mass based on the vehicle's acceleration from a stopped state and an incline or decline of the ground,

dynamically set safety brake distances for the vehicle based on the payload or towing mass,

detect if the payload or towing mass has changed, and

if a change is detected, automatically adjust
- the speed of the vehicle, based on preset safety brake distance information associated with the detected different payload mass and/or

- a size of the safety zone in order to avoid collision with any obstacles.
The automatically guided vehicle of claim 1, wherein the control system includes multiple sub-control systems.
The automatically guided vehicle of claim 1 or 2, wherein a cart attaching mechanism is mounted on said robot body for coupling a cart to said vehicle.
The automatically guided vehicle of any one of the claims 1 to 3, wherein the preset safety brake distance or size of the safety zone is provided as a user input or a protocol stored in the control system.
The automatically guided vehicle of any one of the claims 1 to 3, wherein the preset safety brake distance or size of the safety zone is based on calculating the payload through a measured acceleration and deceleration procedure.
The automatically guided vehicle of claim 5, wherein the acceleration and deceleration is determined by the control system through the following steps
accelerate the vehicle to drive with a known predetermined motor torque and, from a motor/wheel encoder input, calculate the acceleration of the vehicle, and

apply a predetermined period of braking or free running to calculate the deceleration.
The automatically guided vehicle of any one of the claims 1 to 6, wherein a proximity sensor is mounted on the robot body for detecting if a cart is towed by the vehicle or if additional payload has been loaded onto the vehicle.
The automatically guided vehicle of claim 7, wherein the detection with the proximity sensor is based on light, capacitance, inductance or mechanical movement.
The automatically guided vehicle of any one of the claims 1 to 8, wherein payload mass towed and/or carried by the vehicle is detected with a mass sensor that determines the mass of the payload.
The automatically guided vehicle of claim 9, wherein the mass sensor is an instrument for weighing, such as a load cell, scale or balance.